linux-stable.git/kernel/printk, branch v3.16.40

printk: fix parsing of "brl=" option

2016-11-20T01:17:18+00:00

commit ae6c33ba6e37eea3012fe2640b22400ef3f2d0f3 upstream.

Commit bbeddf52adc1 ("printk: move braille console support into separate
braille.[ch] files") moved the parsing of braille-related options into
_braille_console_setup(), changing the type of variable str from char*
to char**.  In this commit, memcmp(str, "brl,", 4) was correctly updated
to memcmp(*str, "brl,", 4) but not memcmp(str, "brl=", 4).

Update the code to make "brl=" option work again and replace memcmp()
with strncmp() to make the compiler able to detect such an issue.

Fixes: bbeddf52adc1 ("printk: move braille console support into separate braille.[ch] files")
Link: http://lkml.kernel.org/r/20160823165700.28952-1-nicolas.iooss_linux@m4x.org
Signed-off-by: Nicolas Iooss 
Cc: Joe Perches 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Ben Hutchings

printk: do cond_resched() between lines while outputting to consoles

2016-02-02T19:09:51+00:00

commit 8d91f8b15361dfb438ab6eb3b319e2ded43458ff upstream.

@console_may_schedule tracks whether console_sem was acquired through
lock or trylock.  If the former, we're inside a sleepable context and
console_conditional_schedule() performs cond_resched().  This allows
console drivers which use console_lock for synchronization to yield
while performing time-consuming operations such as scrolling.

However, the actual console outputting is performed while holding
irq-safe logbuf_lock, so console_unlock() clears @console_may_schedule
before starting outputting lines.  Also, only a few drivers call
console_conditional_schedule() to begin with.  This means that when a
lot of lines need to be output by console_unlock(), for example on a
console registration, the task doing console_unlock() may not yield for
a long time on a non-preemptible kernel.

If this happens with a slow console devices, for example a serial
console, the outputting task may occupy the cpu for a very long time.
Long enough to trigger softlockup and/or RCU stall warnings, which in
turn pile more messages, sometimes enough to trigger the next cycle of
warnings incapacitating the system.

Fix it by making console_unlock() insert cond_resched() between lines if
@console_may_schedule.

Signed-off-by: Tejun Heo 
Reported-by: Calvin Owens 
Acked-by: Jan Kara 
Cc: Dave Jones 
Cc: Kyle McMartin 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Luis Henriques

printk: prevent userland from spoofing kernel messages

2015-12-13T17:49:52+00:00

commit 3824657c522f19f85a76bd932821174a5557a382 upstream.

The following statement of ABI/testing/dev-kmsg is not quite right:

   It is not possible to inject messages from userspace with the
   facility number LOG_KERN (0), to make sure that the origin of the
   messages can always be reliably determined.

Userland actually can inject messages with a facility of 0 by abusing the
fact that the facility is stored in a u8 data type.  By using a facility
which is a multiple of 256 the assignment of msg->facility in log_store()
implicitly truncates it to 0, i.e.  LOG_KERN, allowing users of /dev/kmsg
to spoof kernel messages as shown below:

The following call...
   # printf '<%d>Kernel panic - not syncing: beer empty\n' 0 >/dev/kmsg
...leads to the following log entry (dmesg -x | tail -n 1):
   user  :emerg : [   66.137758] Kernel panic - not syncing: beer empty

However, this call...
   # printf '<%d>Kernel panic - not syncing: beer empty\n' 0x800 >/dev/kmsg
...leads to the slightly different log entry (note the kernel facility):
   kern  :emerg : [   74.177343] Kernel panic - not syncing: beer empty

Fix that by limiting the user provided facility to 8 bit right from the
beginning and catch the truncation early.

Fixes: 7ff9554bb578 ("printk: convert byte-buffer to variable-length...")
Signed-off-by: Mathias Krause 
Cc: Greg Kroah-Hartman 
Cc: Petr Mladek 
Cc: Alex Elder 
Cc: Joe Perches 
Cc: Kay Sievers 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
[ kamal: backport to 3.13-stable: retain local 'int i' ]
Signed-off-by: Kamal Mostafa 
Signed-off-by: Luis Henriques

security_syslog() should be called once only

2015-07-15T09:01:30+00:00

commit d194e5d666225b04c7754471df0948f645b6ab3a upstream.

The final version of commit 637241a900cb ("kmsg: honor dmesg_restrict
sysctl on /dev/kmsg") lost few hooks, as result security_syslog() are
processed incorrectly:

- open of /dev/kmsg checks syslog access permissions by using
  check_syslog_permissions() where security_syslog() is not called if
  dmesg_restrict is set.

- syslog syscall and /proc/kmsg calls do_syslog() where security_syslog
  can be executed twice (inside check_syslog_permissions() and then
  directly in do_syslog())

With this patch security_syslog() is called once only in all
syslog-related operations regardless of dmesg_restrict value.

Fixes: 637241a900cb ("kmsg: honor dmesg_restrict sysctl on /dev/kmsg")
Signed-off-by: Vasily Averin 
Cc: Kees Cook 
Cc: Josh Boyer 
Cc: Eric Paris 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Luis Henriques

console: Fix console name size mismatch

2015-03-18T15:07:22+00:00

commit 30a22c215a0007603ffc08021f2e8b64018517dd upstream.

commit 6ae9200f2cab7 ("enlarge console.name") increased the storage
for the console name to 16 bytes, but not the corresponding
struct console_cmdline::name storage. Console names longer than
8 bytes cause read beyond end-of-string and failure to match
console; I'm not sure if there are other unexpected consequences.

Signed-off-by: Peter Hurley 
Signed-off-by: Greg Kroah-Hartman 
Signed-off-by: Luis Henriques

kernel/printk/printk.c: fix faulty logic in the case of recursive printk

2014-10-05T20:41:07+00:00

commit 000a7d66ec30898f46869be01ab8205b056385d0 upstream.

We shouldn't set text_len in the code path that detects printk recursion
because text_len corresponds to the length of the string inside textbuf.
A few lines down from the line

    text_len = strlen(recursion_msg);

is the line

    text_len += vscnprintf(text + text_len, ...);

So if printk detects recursion, it sets text_len to 29 (the length of
recursion_msg) and logs an error.  Then the message supplied by the
caller of printk is stored inside textbuf but offset by 29 bytes.  This
means that the output of the recursive call to printk will contain 29
bytes of garbage in front of it.

This defect is caused by commit 458df9fd4815 ("printk: remove separate
printk_sched buffers and use printk buf instead") which turned the line

    text_len = vscnprintf(text, ...);

into

    text_len += vscnprintf(text + text_len, ...);

To fix this, this patch avoids setting text_len when logging the printk
recursion error.  This patch also marks unlikely() the branch leading up
to this code.

Fixes: 458df9fd4815b478 ("printk: remove separate printk_sched buffers and use printk buf instead")
Signed-off-by: Patrick Palka 
Reviewed-by: Petr Mladek 
Reviewed-by: Jan Kara 
Acked-by: Steven Rostedt 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

kernel/printk/printk.c: revert "printk: enable interrupts before calling console_trylock_for_printk()"

2014-07-03T16:21:54+00:00

Revert commit 939f04bec1a4 ("printk: enable interrupts before calling
console_trylock_for_printk()").

Andreas reported:

: None of the post 3.15 kernel boot for me. They all hang at the GRUB
: screen telling me it loaded and started the kernel, but the kernel
: itself stops before it prints anything (or even replaces the GRUB
: background graphics).

939f04bec1a4 is modest latency reduction.  Revert it until we understand
the reason for these failures.

Reported-by: Andreas Bombe 
Cc: Jan Kara 
Cc: Steven Rostedt 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

kernel/printk: use symbolic defines for console loglevels

2014-06-04T23:54:17+00:00

... instead of naked numbers.

Stuff in sysrq.c used to set it to 8 which is supposed to mean above
default level so set it to DEBUG instead as we're terminating/killing all
tasks and we want to be verbose there.

Also, correct the check in x86_64_start_kernel which should be >= as
we're clearly issuing the string there for all debug levels, not only
the magical 10.

Signed-off-by: Borislav Petkov 
Acked-by: Kees Cook 
Acked-by: Randy Dunlap 
Cc: Joe Perches 
Cc: Valdis Kletnieks 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

printk: report dropping of messages from logbuf

2014-06-04T23:54:17+00:00

If the log ring buffer becomes full, we silently overwrite old messages
with new data.  console_unlock will detect this case and fast-forward the
console_* pointers to skip over the corrupted data, but nothing will be
reported to the user.

This patch hijacks the first valid log message after detecting that we
dropped messages and prefixes it with a note detailing how many messages
were dropped.  For long (~1000 char) messages, this will result in some
truncation of the real message, but given that we're dropping things
anyway, that doesn't seem to be the end of the world.

Signed-off-by: Will Deacon 
Acked-by: Peter Zijlstra 
Cc: Kay Sievers 
Cc: Jan Kara 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

printk: rename printk_sched to printk_deferred

2014-06-04T23:54:17+00:00

After learning we'll need some sort of deferred printk functionality in
the timekeeping core, Peter suggested we rename the printk_sched function
so it can be reused by needed subsystems.

This only changes the function name. No logic changes.

Signed-off-by: John Stultz 
Reviewed-by: Steven Rostedt 
Cc: Jan Kara 
Cc: Peter Zijlstra 
Cc: Jiri Bohac 
Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds